In the mining industry, it is customary to support the roof of each mine by initially drilling holes in the rock strata in a predetermined pattern, and then installing roof bolts into the newly drilled holes. Today's roof bolts are generally installed into the drilled hole with a resin adhesive and the like to further secure the bolt within the drilled hole. Additionally, these bolts are accompanied by a metal plate that is positioned to support the rock strata to prevent the collapse of the mine roof.
In order to drill holes in the rock strata, a conventional roof drilling machine is utilized. Typically, these drilling machines include a drive end and utilize drill steel members and a carbide insert or drill bit, generally 1" in diameter, attached to one end of the final drill steel member to drill the holes in the mine roof. These drill steel members are generally coupled on the other end, e.g. the drive end, by a chuck located on the drilling machine. This attachment provides a means for rotating the drill member and thus the drill bit to remove material and debris from the drilled hole. To facilitate the removal of material and debris from the drilled hole, many drilling machines incorporate a vacuum suction collection system wherein the drill steel member is constructed from a hollow steel bar, the drill bit is configured to remove debris via a passageway located within the bit, and the vacuum system collects the debris as it is passed through the passageway of the drill bit and the hollow drill steel member during drilling of the rock strata.
In mines having relatively high seams of minerals, such as coal, the drill steel members are designed and manufactured to a sufficient length for drilling the desired depth, generally three to six feet, without the need to replace or extend the drill steel member. However, in low height mines, it becomes necessary to initially drill the hole with a shorter drill steel member, often known as a starter, and then replace the starter with additional sections of drill steel, such as drivers, extensions and finishers, to drill the remaining desired depth of the hole. These additional sections are often joined together by various component parts that generally include a drill bit seat, a male and a female connector, and a drive end component. These components are typically attached or configured to the ends of the drill steel members or sections by various methods discussed below.
In accordance with one conventional manufacturing technique, a drill steel section is cut to the desired drilling length for a particular member and then the ends of the section are typically beveled to facilitate welding of a component part onto the corresponding end of the drill steel section. The individual components are initially cast or otherwise fabricated by various well-known processes and then welded directly to an appropriate end of the corresponding drill steel section. Although these completed drill steel members, including the starter, driver, extension and finisher, are generally easy to manufacture, many drawbacks for this manufacturing method exist.
First, the effects of heat produced during the welding of components to drill steel sections results in the production of stress fractures, cracks and other residual stresses as a result of the intense heating (welding temperatures can exceed hundreds of degrees of Fahrenheit) and cooling of the steel. These fractures and cracks are produced not at the heat point but typically at the transfer points, or heat-affected zones, located on both sides of the heat point. Additionally, in the current industry, the joining of the components to the drill steel generally requires manual labor to assemble the parts. This assembly process results in variability in alignment of the component parts to the drill sections, and thus in the alignment of one drill steel member, such as a driver, when joined to another drill steel member, such as a finisher. Further, inconsistencies from weld to weld often occur which not only detrimentally affects the quality of the product but also the safety of the product during use. These inconsistencies include, for example, the variability in the type of wire selected, the particular gas utilized, the particular heat settings selected, and the relative experience and ability of the individual welder. As one skilled in the art will appreciates, these variables have a tremendous impact on the overall quality of the welded products and can thus detrimentally affect the performance of those members.
As one skilled in the art will appreciate, the potential for misalignment as well as the production of stress fractures and cracks around the transfer point can lead to a premature failure of one or more of the drill steel members and thus result in unsafe working conditions. An extremely critical aspect of the drilling process is that the drilled hole needs to be truly centered, e.g., as straight as possible, as indicated by a smooth rotation of the drill steel members by the drilling machine. As one skilled in the art will appreciate, this truly centered requirement is even more critical in today's industry due to the operation of drill machines at higher and ever-increasing drilling speeds. Once the drill member is inserted well within the depths of the drilling hole, the opportunity for lateral movement of the drill steel member within the hole is minimal. Since the drilling machine is stationary, any stresses or forces generated by misalignment of the drill steel members will be imparted on the weakest point of the drilling system, e.g., the existing stress fracture or crack or misaligned area, and thus the drill steel member will prematurely fail. Often this failure occurs in the area proximate the drive end of the drilling machine and near the drilling machine operator, an extremely hazardous and unsafe condition. Therefore, as one skilled in the art will appreciate, these problems result in higher production costs due to excessive component usage and equipment downtime
Due to these safety hazards, as well as increased operating costs, various other methods have been developed in an attempt to minimize the potential for the production of fractures or cracks and misalignment problems. U.S. Pat. No. 4,299,510, issued to Emmerich et al. on Nov. 10, 1981, generally discloses a two-step process utilizing hot upset forging to eliminate the need for welding the component directly to one end of the drill steel section. U.S. Pat. No. 4,453,854, issued to Emmerich et al. on Jun. 12, 1984, generally discloses a one-hit hot forming process for producing a drill steel member. Other known forging methods, e.g., open and closed die forging and back extrusion forging, can be utilized for the manufacturing of drill steel members. When utilizing one of the above methods, generally, a manufacturer cuts the drill steel section to an appropriate length (the desired drilling length plus the additional length needed for forging the component part). Once cut, the ends of the section are heated to extreme temperatures (which may exceed hundreds of degrees Fahrenheit) and then placed into a forging press, wherein the component part is pounded out from the hot material. The advantages of these forging processes include cheaper manufacturing costs due to the processing of the component parts directly from the heated ends of the drill steel sections as well as the use of automation in the forging process. As a result of a reduction in the opportunities for misalignment of component parts, forged drill steel members have been known to outperform the life span of welded drill steel members by a factor of 2 to 3 times longer.
However, various disadvantages also exist with forged steel products. As discussed above, the component parts are formed from the heating and shaping of the steel sections. Forging heat, as one skilled in the art will appreciate, is a wider-spread heat than that applied from welding processes, and is generally significantly hotter than the welding process, such that larger heat-affected zones can be generated. Additionally, although the component part is created directly within the end section of the drill steel, the tolerances associated with the forging process still provide opportunities for misalignment. Although the misalignment of forging products can be significantly less than that of welded products, the combination of misalignment and the use of extreme heat in the process, which can produce residual stresses or cracks, still leads to premature failures of the drill steel members.
In an attempt to minimize these problems, many manufacturers will utilize a thicker-walled tubing for the drill steel sections and members. The outside diameter of the drill steel members is generally produced to 7/8", due to the necessity during drilling operations to drill holes of a particular diameter to accommodate the standard-sized roof bolts utilized throughout the mining industry. Therefore, in order for manufacturers to obtain a thicker-walled tubing, the inner diameter of the drill steel member must be decreased. This corresponding decrease in the inner diameter of the drill steel member results in a decrease in the efficiency of the vacuum collection system, and thus a decrease in the drilling rate and performance of these prior art drill members.
Yet another drawback of the forging methods described above occurs during the forming of female component parts used for coupling of one drill steel member, such as a starter, to another drill steel member, such as a finisher. As discussed, when using forging methods, typically, an appropriate end of a drill steel section is heated to an extreme temperature and then placed into a forging press to pound out the component part, such as the female component, from the hot material. The pounding out of the component has a tendency to produce a female component with a diameter larger than the 7/8" steel tube utilized, generally approaching 1" in size. Due to the 1" diameter hole being drilled by the carbide drill bit, very little clearance exists between the female component part and the drilled hole. As one skilled in the art will appreciate, this lack of clearance often causes severe dragging on the drill system as a result of friction generated between the rotating component part and the inner walls of the drilled hole. In addition, the friction generated has a tendency to heat up the component parts and further accelerate the deterioration and wear of the drill steel members, thus resulting in premature failures.
Thus, a long felt need exist for an improved drill steel member that provides a longer product life and a significant reduction in premature failures during operation. Furthermore, there exists a long felt need for drill steel members that are not only safer for the mine worker and for the industry but also provide improved drilling performance, such as, for example by providing improved vacuum collection efficiency and improved drill centering and alignment, thus resulting in a more desirable drill steel member.